Catalyst feed systems and methods for using the same

ABSTRACT

Catalyst feed systems and processes utilizing such systems are described herein. Some embodiments disclosed herein relate to a process for improving the flowability of catalyst in a catalyst feed system, including providing a catalyst feed vessel with at least one heat exchange system for maintaining the catalyst system temperature below a critical flow temperature. Also disclosed is a catalyst feed system for the polymerization of olefins including a catalyst feed vessel; and a heat exchange system for maintaining a temperature of a catalyst within the catalyst feed vessel. Additionally disclosed is a process for polymerization of olefins including maintaining a supported catalyst in a catalyst feed vessel below a critical flow temperature of the catalyst; feeding the catalyst to a polymerization reactor; and contacting the catalyst with an olefin to form a polyolefin.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/811,482, filed Sep. 2, 2010, which is a National Stage Applicationunder 35 U.S.C. §371 of International Application No. PCT/US2008/013730,filed Dec. 15, 2008, which claimed the benefit of U.S. ProvisionalApplication Ser. No. 61/010,238, filed Jan. 7, 2008, the disclosures ofwhich are incorporated by reference in their entirety.

FIELD OF THE INVENTION

Embodiments disclosed herein relate generally to catalyst feed systems.More particularly, embodiments disclosed herein relate to catalyst feedsystems for polymerization processes. Even more particularly,embodiments disclosed herein relate to improved flowability of catalystsystems in catalyst feed systems and catalyst storage vessels for olefinpolymerization processes.

BACKGROUND

Advances in polymerization and catalysis have resulted in the capabilityto produce a plethora of new polymers having improved physical andchemical properties. These new polymers have proved useful in producinga wide variety of superior products with new applications. With thedevelopment of new catalysts, the variety of polymerization types(solution, slurry, high pressure, or gas phase) available for producinga particular polymer has also been greatly expanded. Advances inpolymerization technology have thus resulted in more efficient andhighly productive processes which have proved economically advantageous.Illustrative of these advances is the development of technologyutilizing supported catalyst systems for the heterogeneous catalysis ofolefin polymerizations. These heterogeneous catalyst systems provide asurface area for catalysis, and are typically prepared by deposition ofreactive catalytic moieties on a particulate support, usually aninorganic oxide. There are a variety of different methods described inthe art for supporting catalytic moieties on supports for use in slurryor gas phase polymerization processes.

For example, heterogeneous catalysts, such as supported Ziegler-Natta orchromium-based catalysts, have had significant impact on the polyolefinindustry. Supported Ziegler-Natta catalysts afford high activity andhigh stereo-regular content in olefin polymerization while supportedchromium-based catalyst systems typically produce polyolefins with anarrow molecular weight distribution and high molecular weight. Coupledwith advantages over homogeneous catalysts, such as increased thermalstability, ease of separation, and no solvent limitations, heterogeneouscatalyst systems may be industrially advantageous. Such catalyst systemsopened scientific floodgates, leading to an explosion of new chemistry,new processes, and new products in the polyolefin industry.

However, as with the advent of any new technology, new challenges arepresented with the heterogenization of catalyst systems. For example,heterogeneous catalyst systems are theoretically less efficient thantheir homogeneous counterparts because the polymerization reaction mustnecessarily take place on the surface of the catalyst. Any catalystmoiety not present at the surface may remain unused, whereas all themolecules in a homogeneous catalyst are theoretically available.Further, heterogeneous catalyst systems tend to be more sensitive topoisoning, such as by soft ligands and the oxygen content and humidityof air, than homogeneous catalysts. As such, heterogeneous catalystsystems are usually handled under highly inert, dry, and oxygen freeatmospheres. Yet further, circulation of heterogeneous catalyst systemsthrough the polymerization system poses unique problems. Whereashomogeneous catalysts are usually introduced as a solution in a wetfeed, heterogeneous catalyst systems may be introduced as a dry feed.The use of a dry catalyst feed presents several advantages over a wetfeed, such as ease of handling and conservation of solvent. Thus, thedry feed of a supported catalyst system may provide both economic andenvironmental advantages to a polyolefin manufacturer.

In a dry catalyst feed process, it is desirable that the heterogeneouscatalyst system flow freely through catalyst feeders and feed lines. Anumber of catalyst feed systems for gas phase reactors are known tothose skilled in the art. Well known systems include systems including acatalyst storage vessel connected to a feed chamber which is in turnconnected to a gas phase reactor. The catalyst storage vessel, feedchamber, and gas phase reactor may be connected to each other by fillingand emptying valves. Typically, a heterogeneous catalyst system isconveyed from the storage vessel through the catalyst feed system to thereactor by maintaining the reactor at a pressure lower than that in thecatalyst feed system. Valves incorporated in such systems allow a givenquantity of heterogeneous catalyst system to move from the storagevessel to a feed chamber or metering device and then to the reactor.

U.S. Pat. No. 4,162,894 describes a pressure equalized feed systemincorporating a ball check feed valve and a downstream positive shut-offvalve for controlling intermittent feed of heterogeneous catalystsystem. U.S. Pat. No. 4,687,381 describes a feed system using a shut-offvalve and metering device for periodic delivery of powderedheterogeneous catalyst system. These, and other conventional catalystfeed systems, however, may not overcome the problems caused by poorcatalyst flow.

The flow properties of a heterogeneous catalyst system are dependent ona multitude of factors, such as the nature of the catalytic moiety andthe nature of the support, among other factors. For example,heterogeneous catalyst systems, including a carboxylate metal salt inconjunction with a supported metallocene catalyst system such asdescribed in U.S. Pat. Nos. 6,306,984 and 6,300,436 substantiallyimprove process operability, but have sticky or statically inclinedparticulate flow. Pre-polymerized catalysts, such as described in U.S.Pat. No. 4,579,836, made by treating the catalyst with a small amount ofmonomer under polymerization conditions, may demonstrate improvedcatalyst particle strength and product characteristics, but may have aconcomitant degradation in catalyst flow properties.

Heterogeneous catalyst systems with poor flow are more difficult to feedto a reactor, and may prevent the desired smooth and continuousintroduction of catalyst into the reactor. Poorly flowing heterogeneouscatalyst systems may also stick to walls of catalyst feed vessels,feeders, and feed lines, causing buildup and possible clogging of feedlines. Buildup of residual catalyst system in feed lines interferes withcontrol of delivery, and ultimately process control. Further, poorlyflowing heterogeneous catalyst systems may impair accurate delivery ofthe desired catalyst system amount to the polymerization reactor. Thismay result in poor polymerization efficiency and low production.Ineffective catalyst delivery, therefore, affects system performance,stability, and, ultimately, the polymer product.

The myriad of problems caused by poorly flowing catalyst systemssignificantly impairs process operability and efficiency, in some casesto the point of reactor shutdown. Where the buildup proceeds to theextent that feed lines are clogged, the polymerization system may haveto be taken off line to clean the clogged lines. Frequent repair and/orreplacement of system valves and clogged lines can prove time-consumingand expensive. Repair of clogged lines and valves results in reactordowntime, increased personnel hours, and replacement of parts, all ofwhich add to the cost of the process, and may result in a significanteconomic loss to the polymer manufacturer.

Solutions to poorly flowing dry heterogeneous catalyst systems have beenaddressed by modifying the method of preparation of the catalyst system.For example, the catalyst system components may be combined in aparticular order; the ratio of the various catalyst system componentsmay be manipulated; the contact time and/or temperature when combiningthe components while forming a catalyst system may be varied; oradditional compounds may be added to the catalyst system. Examples ofthese include: WO 96/11961 discusses an antistatic agent as a componentof a supported catalyst system; U.S. Pat. Nos. 5,332,706 and 5,473,028disclose incipient impregnation as a particular technique for forming acatalyst system; U.S. Pat. Nos. 5,427,991 and 5,643,847 describe thechemical bonding of non-coordinating anionic activators to supports;U.S. Pat. No. 5,492,975 discusses polymer bound metallocene catalystsystems; and U.S. Pat. No. 6,680,276 discusses a composition of acarboxylate metal salt in combination with a heated polymerizationcatalyst system to improve the catalyst system flow and operability ofthe catalyst system.

Other solutions have been directed towards the catalyst feed system. Forexample, U.S. Pat. No. 5,433,924 is directed towards using filterspositioned to vent the fill chamber. The positioning of the filterprovides a pressure differential to encourage poorly flowing catalystsystem to flow through the feed lines, and provides a means for removingand recycling residual catalyst system. U.S. Pat. No. 4,690,804describes the use of a ball check feed valve for the transfer of polymercoated catalyst system.

Some of the techniques discussed above for remedying poor catalystsystem flow may affect catalyst system productivity, catalyst systemactivity, may not work for particular catalyst system types, may addsignificant cost to the catalyst system manufacture process, and maycause additional problems such as sheeting and fouling during thepolymerization process. Accordingly, there exists a need for methods,processes, and systems to improve catalyst system flow.

SUMMARY

In one aspect, embodiments disclosed herein relate to a process forimproving the flowability of catalyst in a catalyst feed system,including providing a catalyst feed vessel with at least one heatexchange system for maintaining catalyst system temperature below acritical flow temperature.

In another aspect, embodiments disclosed herein relate to a catalystfeed system for the polymerization of olefins including a catalyst feedvessel; and a heat exchange system for maintaining a temperature of acatalyst within the catalyst feed vessel.

In yet another aspect, a process for polymerization of olefins includingmaintaining a supported catalyst in a catalyst feed vessel below acritical flow temperature of the catalyst; feeding the catalyst to apolymerization reactor; and contacting the catalyst with an olefin toform a polyolefin.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cooled catalyst feed system, according to embodimentsdescribed herein.

FIG. 2 is another cooled catalyst feed system, according to embodimentsdescribed herein.

DETAILED DESCRIPTION

Before the present compounds, components, compositions, and/or methodsare disclosed and described, it is to be understood that unlessotherwise indicated this invention is not limited to specific compounds,components, compositions, reactants, reaction conditions, ligands,metallocene structures, or the like, as such may vary, unless otherwisespecified. It is also to be understood that the terminology used hereinis for the purpose of describing particular embodiments only and is notintended to be limiting.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified. Thus, for example, reference to “aleaving group” as in a moiety “substituted with a leaving group”includes more than one leaving group, such that the moiety may besubstituted with two or more such groups. Similarly, reference to “ahalogen atom” as in a moiety “substituted with a halogen atom” includesmore than one halogen atom, such that the moiety may be substituted withtwo or more halogen atoms, reference to “a substituent” includes one ormore substituents, reference to “a ligand” includes one or more ligands,and the like.

Generally, embodiments disclosed herein relate to the improvement ofheterogeneous catalyst feed systems and flow of the catalyst systemwithin the feed system. In one aspect, embodiments disclosed hereinrelate to a catalyst feed system for the polymerization of olefinsincluding a catalyst feed vessel, a catalyst feeder for aliquoting thecatalyst system, and a system for maintaining the catalyst feed vesseltemperature. In yet another aspect, embodiments disclosed herein relateto a process for polymerization of olefins including cooling thecatalyst shipping containers, cooling the catalyst transport system fromthe shipping containers to the catalyst feed system, and cooling thecatalyst feed system.

As used hereafter, “flowability” refers to the ability of theheterogeneous catalyst system to flow. Good flowability refers to theability of heterogeneous catalyst systems to flow freely andconsistently. Non-flowing or poorly flowing catalyst systems have poorflowability. Heterogeneous catalyst systems can therefore range fromfree-flowing powders having good flowability to non-flowing powdershaving poor or no flowability. Flowability is a complex andmultidimensional property, and may be affected by both material physicalproperties of the catalyst system and the equipment used for handling,storing, or processing the catalyst system. Factors that affectflowability may include particle size and homogeneity, nature of thecatalytic moiety supported on the solid support, humidity, temperature,and static generated by the flow of the catalyst system over theinterior walls of the catalyst feed system, among others.

Flowability may be assessed, for example, by monitoring the pressuredifferential across the catalyst pick-up block, using variousinstruments known to one of skill in the art, such as pressure gages,differential pressure gages, etc. The catalyst pick-up block fluidlyconnects the catalyst feed vessel to the catalyst feed line which goesto the polymerizations reactor. The pressure differential across thepick-up block measures the ease of transfer of the catalyst from thecatalyst feed vessel to the catalyst feed line. If the catalyst systemexhibits clumping or tackiness leading to poor flow, the uptake of thecatalyst by the catalyst pick-up line may be affected. This may in turnbe reflected in poor pressure differential across the catalyst pick-upblock. Accordingly, a catalyst with good flowability is one whichdemonstrates acceptable pressure differential. Where very little or nopressure differential is observed, this is indicative of possibleclogging and the catalyst is deemed to possess poor flowability.

As used hereafter, “aliquoting” refers to designating a portion, part,or sample of a chemical composition. For example, aliquoting of acatalyst system would refer to the designation of a portion, part, orsample of that catalyst system.

The inventors of embodiments of the present disclosure have found thatthe temperature of the catalyst feed system is a critical parameter tothe flowability of some catalyst systems. At elevated temperatures, somecatalyst systems have been observed to exhibit poor flowability, whichmay adversely affect catalyst system feed and reactor operations. Forexample, particular metallocene catalyst systems may exhibit poorflowability at or above a temperature of about 29° C. Elevated catalystsystem temperatures may be encountered during handling, storage, and/ortransport of the catalyst system, each of which may contribute or causepoor flowability of a catalyst system. Without being bound to theory,there are several possible causes, inclusive of ambient heat and heat offriction, for undesirable elevated temperatures encountered during thehandling, storage, and/or transportation processes. Temperatures abovewhich a catalyst system exhibits decreased or poor flowability will bereferred to herein as the “critical flow temperature” of the catalystsystem.

For example, in tropical climates, and during warmer times of the year,catalyst containers and feed systems may warm above critical flowtemperatures due to ambient heat. Catalyst system temperatures may alsobe influenced by a multitude of factors other than ambient temperature,such as solar heat flux, especially under peak summer conditions;convective heat gain at wind velocities around the elevated structuresof the storage, holding, feeding, or processing vessels; radiant heatgain from the reactor, flares, machinery, and other equipment atelevated temperatures; and conduction through insulation or pipe wallsin contact with media at elevated temperatures. In some instances, thetemperature of the catalyst storage vessels and/or feed system may riseto 40° C. or higher. Exposure of the catalyst system to these elevatedtemperatures may lead to clumping, increased static and poorflowability, which in turn may lead to clogging of feed vessels and feedlines, as discussed above.

Catalyst systems may also experience heat gain through loading and flowthrough the catalyst feed system. As the heterogeneous catalyst systemflows through the catalyst feed vessel, valves, and feed lines, theparticles may impact surfaces of the catalyst feed system as well asother catalyst system particles. The kinetic energy of the movingparticles may be converted into heat of friction, which may contributeto increasing the temperature of the catalyst system within the catalystfeed system.

Ambient heat, alone or coupled with heat of friction, may cause elevatedcatalyst feed temperatures, often well above the critical flowtemperature of many catalyst systems. Heterogeneous catalyst systemsexposed to these elevated temperatures during feed processes and/orduring storage may become sticky, clumped, or statically inclined.

Applicants have advantageously found that by maintaining the temperatureof the catalyst feed system, or portions thereof, below the criticalflow temperature of a catalyst system may improve the flowability of thecatalyst system through the catalyst feed system. Applicants have alsofound that regulating the temperature of the catalyst system at allstages of handling, inclusive of storage and transportation, may improvecatalyst system flowability. In various embodiments of this disclosure,improved flowability has been observed where the catalyst feed system,or portions thereof, is maintained, for example, below 29° C., below 27°C., below 25° C., below 15° C., and below 10° C.

The term “heterogeneous catalyst systems” typically refers to a catalystwhich is present in a different phase from the reactants. In embodimentsherein, heterogeneous catalyst system refers to solid or supportedcatalysts. Accordingly, the heterogeneous catalyst systems undergoparticulate flow through the catalyst feed systems of the presentdisclosure. The heterogeneous catalyst systems of the present disclosuremay include any of the kinds known to be used for polymerization oroligomerization. In some embodiments, the heterogeneous catalyst systemmay be of the types used in the polymerization or oligomerization ofolefins. For example, the heterogeneous catalyst system may be acatalyst or a “catalyst system,” as typically used in this type ofpolymerization.

The term “catalyst system” includes at least one “catalyst component”and at least one “activator” or “cocatalyst,” and alternatively at leastone other component, such as, for example, at least one “continuityadditive.” The catalyst system also includes other components, such assupports, and is not limited to the catalyst component and/or activatoralone or in combination. The catalyst system may include any number ofcatalyst components in any combination, as well as any activator in anycombination.

The term “catalyst component” includes any compound that, onceappropriately activated, is capable of catalyzing the polymerization oroligomerization of olefins. In some embodiments, the catalyst componentincludes at least one Group 3 to Group 12 atom and optionally at leastone leaving group bound thereto. As used herein, in reference toPeriodic Table “Groups” of Elements, the “new” numbering scheme for thePeriodic Table Groups is used as in the CRC Handbook of Chemistry andPhysics (David R. Lide, ed., CRC Press, 81^(st) ed., 2000).

The catalyst or catalyst system may include Ziegler-Natta catalysts,chromium-based catalysts, metallocene catalysts and other single-sitecatalysts, Group 15-containing catalysts, and bimetallic catalysts. Thecatalyst or catalyst system may also include AlCl₃, cobalt, iron,palladium, chromium/chromium oxide or “Phillips” catalysts. Any catalystor catalyst system may be used alone or in combination with the others.In one or more embodiments, a “mixed” catalyst system is preferred.

Illustrative non-metallocene Ziegler-Natta catalyst compounds aredisclosed in ZIEGLER CATALYSTS 363-386 (G. Fink, R. Mulhaupt and H. H.Brintzinger, eds., Springer-Verlag 1995); or in EP 103 120; EP 102 503;EP 0 231 102; EP 0 703 246; RE 33,683; U.S. Pat. No. 4,302,565; U.S.Pat. No. 5,518,973; U.S. Pat. No. 5,525,678; U.S. Pat. No. 5,288,933;U.S. Pat. No. 5,290,745; U.S. Pat. No. 5,093,415 and U.S. Pat. No.6,562,905. Examples of such catalysts include those including Group 4, 5or 6 transition metal oxides, alkoxides and halides, or oxides,alkoxides and halide compounds of titanium, zirconium or vanadium;optionally in combination with a magnesium compound, internal and/orexternal electron donors (alcohols, ethers, siloxanes, etc.), aluminumor boron alkyl and alkyl halides, and inorganic oxide supports. Examplesof conventional Ziegler-Natta catalysts are discussed in U.S. Pat. Nos.4,115,639, 4,077,904, 4,482,687, 4,564,605, 4,721,763, 4,879,359 and4,960,741. The conventional Ziegler-Natta catalysts that may be usedinclude transition metal compounds from Groups 3 to 17, or Groups 4 to12, or Groups 4 to 6 of the Periodic Table of Elements. Theseconventional Ziegler-Natta catalysts may be represented by the formula:MR_(x), where M is a metal from Groups 3 to 17, or a metal from Groups 4to 6, or a metal from Group 4, or titanium; R is a halogen or ahydrocarbyloxy group; and x is the valence of the metal M. Examples of Rinclude alkoxy, phenoxy, bromide, chloride and fluoride. Examples ofconventional Ziegler-Natta catalysts where M is titanium include TiCl₄,TlBr₄, Ti(OC₂H₅)₃Cl, Ti(OC₂H₅)Cl₃, Ti(OC₄H₉)₃Cl, Ti(OC₃H₇)₂Cl₂,Ti(OC₂H₅)₂Br₂, TiCl₃.⅓AlCl₃ and Ti(OC₁₂H₂₅)Cl₃.

Illustrative chromium-based catalysts include di-substituted chromates,such as CrO₂(OR)₂; where R is triphenylsilane or a tertiarypolyalicyclic alkyl. The chromium catalyst system may further includeCrO₃, chromocene, silyl chromate, chromyl chloride (CrO₂Cl₂),chromium-2-ethyl-hexanoate, chromium acetylacetonate (Cr(AcAc)₃), andthe like.

Other catalysts useful in embodiments of the present disclosure mayinclude Group 15-containing catalysts. The “Group 15-containingcatalyst” may include Group 3 to Group 12 metal complexes, and Group 4metals in a particular embodiment wherein the metal is 2 to 8coordinate, 2 to 4 coordinate in a particular embodiment, thecoordinating moiety or moieties including at least two Group 15 atoms,and up to four Group 15 atoms. In one embodiment, the Group15-containing catalyst component is a complex of a Group 4 metal andfrom one to four ligands such that the Group 4 metal is at least 2coordinate, the coordinating moiety or moieties including at least twonitrogen atoms. Representative Group 15-containing compounds aredisclosed in, for example, WO 99/01460; EP A1 0 893 454; U.S. Pat. No.5,318,935; U.S. Pat. No. 5,889,128; U.S. Pat. No. 6,333,389 B2; and U.S.Pat. No. 6,271,325 B1. In one embodiment, the Group 15-containingcatalyst includes Group 4 imino-phenol complexes, Group 4 bis(amide)complexes, and Group 4 pyridyl-amide complexes that are active to anydegree towards olefin polymerization.

Metallocenes are generally described throughout in, for example, 1 & 2METALLOCENE-BASED POLYOLEFINS (John Scheirs & W. Kaminsky, eds., JohnWiley & Sons, Ltd. 2000); G. G. Hlatky in 181 Coordination Chem. Rev.243-296 (1999) and in particular, for use in the synthesis ofpolyethylene in 1 METALLOCENE-BASED POLYOLEFINS 261-377 (2000). Themetallocene catalyst compounds as described herein include “halfsandwich” and “full sandwich” compounds having one or more Cp ligands(cyclopentadienyl and ligands isolobal to cyclopentadienyl) bound to atleast one Group 3 to Group 12 metal atom, and one or more leavinggroup(s) bound to the at least one metal atom. Hereinafter, thesecompounds will be referred to as “metallocenes” or “metallocene catalystcomponents.” The metallocene catalyst component is supported on asupport material in an embodiment, and may be supported with or withoutanother catalyst component.

The Cp ligands are one or more rings or ring system(s), at least aportion of which includes π-bonded systems, such as cycloalkadienylligands and heterocyclic analogues. The ring(s) or ring system(s)typically comprise atoms selected from the group consisting of Groups 13to 16 atoms, or the atoms that make up the Cp ligands are selected fromthe group consisting of carbon, nitrogen, oxygen, silicon, sulfur,phosphorous, germanium, boron and aluminum and combinations thereof,wherein carbon makes up at least 50% of the ring members.

Catalysts or catalyst systems useful in embodiments of the presentdisclosure may contain “substituted” groups. As used herein, the term“substituted” means that the group described by that term possesses atleast one moiety in place of one or more hydrogens in any position, themoieties selected from such groups as halogen radicals (for example,C_(l), F, Br), hydroxyl groups, carbonyl groups, carboxyl groups, aminegroups, phosphine groups, alkoxy groups, phenyl groups, naphthyl groups,C₁ to C₁₀ alkyl groups, C₂ to C₁₀ alkenyl groups, and combinationsthereof. Examples of substituted alkyls and aryls include, but are notlimited to, acyl radicals, alkylamino radicals, alkoxy radicals, aryloxyradicals, alkylthio radicals, dialkylamino radicals, alkoxycarbonylradicals, aryloxycarbonyl radicals, carbomoyl radicals, alkyl- anddialkyl-carbamoyl radicals, acyloxy radicals, acylamino radicals,arylamino radicals, and combinations thereof For example, the Cpligand(s) may be selected from the group consisting of substituted andunsubstituted cyclopentadienyl ligands and ligands isolobal tocyclopentadienyl, non-limiting examples of which includecyclopentadienyl, indenyl, fluorenyl and other structures. Furthernon-limiting examples of such ligands include cyclopentadienyl,cyclopentaphenanthreneyl, indenyl, benzindenyl, fluorenyl,octahydrofluorenyl, cyclooctatetraenyl, cyclopentacyclododecene,phenanthrindenyl, 3,4-benzofluorenyl, 9-phenylfluorenyl,8-H-cyclopent[a]acenaphthylenyl, 7H-dibenzofluorenyl,indeno[1,2-9]anthrene, thiophenoindenyl, thiophenofluorenyl,hydrogenated versions thereof (e.g., 4,5,6,7-tetrahydroindenyl, or“H₄Ind”), substituted versions thereof, and heterocyclic versionsthereof.

A mixed catalyst system includes at least one metallocene catalystcomponent and at least one non-metallocene component. The mixed catalystsystem may be described as a bimetallic catalyst composition or amulti-catalyst composition. As used herein, the terms “bimetalliccatalyst composition” and “bimetallic catalyst” include any composition,mixture, or system that includes two or more different catalystcomponents, each having a different metal group. The terms“multi-catalyst composition” and “multi-catalyst” include anycomposition, mixture, or system that includes two or more differentcatalyst components regardless of the metals. Therefore, terms“bimetallic catalyst composition,” “bimetallic catalyst,”“multi-catalyst composition,” and “multi-catalyst” will be collectivelyreferred to herein as a “mixed catalyst system” unless specificallynoted otherwise.

Catalysts useful in embodiments of this disclosure may be “activated” bycontact with an “activator” or “cocatalyst.” The term “activator” mayinclude any compound or combination of compounds, supported orunsupported, which can activate a catalyst compound (e.g.,metallocenes), such as by creating a cationic species from the catalystcomponent. Typically, this involves the abstraction of at least oneleaving group (X group in the formulas/structures above) from the metalcenter of the catalyst component. The catalyst components of embodimentsdescribed are thus activated towards olefin polymerization using suchactivators. Embodiments of such activators include Lewis acids such ascyclic or oligomeric poly(hydrocarbylaluminum oxides) and so callednon-coordinating activators (“NCA”) (alternately, “ionizing activators”or “stoichiometric activators”), or any other compound that can converta neutral metallocene catalyst component to a metallocene cation that isactive with respect to olefin polymerization.

For example, Lewis acids may be used to activate the metallocenesdescribed. Illustrative Lewis acids include, but are not limited to,alumoxane (e.g., methyl alumoxane or “MAO”), modified alumoxane (e.g.,modified methyl alumoxane or “MMAO”), tetraisobutyldialuminoxane (e.g.,“TIBAO”), and alkylaluminum compounds. Ionizing activators (neutral orionic) such as tri (n-butyl)ammonium tetrakis(pentafluorophenyl)boronmay be also be used. Further, a trisperfluorophenyl boron metalloidprecursor may be used. Any of those activators/precursors can be usedalone or in combination with the others. MAO and other aluminum-basedactivators are known in the art. Ionizing activators are known in theart and are described by, for example, Eugene You-Xian Chen & Tobin J.Marks, Cocatalysts for Metal-Catalyzed Olefin Polymerization:Activators, Activation Processes, and Structure-Activity Relationships,100(4) CHEMICAL REVIEWS 1391-1434 (2000). The activators may beassociated with or bound to a support, either in association with thecatalyst component (e.g., metallocene) or separate from the catalystcomponent, such as described by Gregory G. Hlatky, HeterogeneousSingle-Site Catalysts for Olefin Polymerization, 100(4) CHEMICAL REVIEWS1347-1374 (2000).

A “continuity additive” may be added to the catalyst systems useful inthis disclosure. Continuity additives may be added to the catalystsystem to reduce sheeting or fouling in the reactor duringpolymerization. Suitable continuity additives for use in the presentinvention comprise one or more compounds selected from alkoxylatedamines, carboxylic acid salts, polysulfones, polymeric polyamines, andsulfonic acids. For example, the continuity additive may comprise any ofethoxylated stearyl amine, aluminum stearate or aluminum oleate ormixtures thereof.

The above references are provided for reference of possible types ofcatalysts which may exhibit poor flowability above a critical flowtemperature. Not all catalysts described in the above references exhibitpoor flowability above a critical flow temperature; however, catalystfeed systems and processes described herein may be used to improve theflowability of the catalysts which do exhibit poor flowability above acritical flow temperature.

In some embodiments, it may be necessary to determine the critical flowtemperature of a catalyst. For example, various catalyst systems mayintermittently exhibit poor flowability, where temperatures above thecritical flow temperature may be a contributing cause to theintermittent flow problems experienced. In such a case, experimentationmay be used to determine the critical flow temperature of the catalyst,and catalyst feed systems as described herein may be used to maintainthe catalyst below the critical feed temperature in a catalyst feedvessel and/or during feeding of the catalyst to a polymerizationreactor.

In some embodiments, the catalysts may include heterogeneousZiegler-Natta catalysts, Phillips catalysts, conventional chromiumcatalysts, Group 15-containing catalysts, and metallocene catalysts, ormixtures thereof In selected embodiments, the catalyst may be XCAT™EZ-100 Metallocene Catalyst or XCAT™ HP-100 Metallocene Catalyst,available from Univation Technologies, LLC, Houston, Tex. XCAT™Metallocene Catalysts, for example, may have a critical flow temperaturewithin the range of 27° C. to 30° C.

Catalysts useful in embodiments disclosed herein are supported on acatalyst support. In some embodiments, the catalysts are deposited ontoconventional catalyst supports, for example, inorganic oxide materials.The inorganic oxide materials which may be used as a support in thecatalyst systems of the present disclosure are porous materials havingwith variable surface area and particle size, for example, a surfacearea in the range of 50 to 1000 square meters per gram, and a particlesize of 0.1 to 200 micrometers. In some embodiments, the particle sizemay be 1 to 50 micrometers. The inorganic oxides which may be usedinclude silica, alumina, thoria, zirconia, aluminum phosphate and othercomparable inorganic oxides, as well as mixtures of such oxides.

In some embodiments of the present disclosure, the catalyst may bedeposited onto conventional catalyst supports. The term “support,” asused herein, refers to any support material, a porous support materialin one exemplary embodiment, including inorganic or organic supportmaterials. The inorganic oxide materials which may be used as a supportin the catalyst compositions of the present invention are porousmaterials having a high surface area, for example, a surface area in therange of 50 to 1000 m² per gram, and a particle size of 20 to 200micrometers. Non-limiting examples of support materials includeinorganic oxides and inorganic chlorides, and in particular suchmaterials as talc, clay, silica, alumina, magnesia, zirconia, ironoxides, boria, calcium oxide, zinc oxide, barium oxide, thoria, aluminumphosphate gels, glass beads, and polymers such as polyvinylchloride andsubstituted polystyrene, functionalized or crosslinked organic supportssuch as polystyrene divinyl benzene polyolefins or polymeric compounds,and mixtures thereof, and graphite, in any of its various forms.

In some embodiment, desirable carriers may be inorganic oxides thatinclude Group 2, 3, 4, 5, 13 and 14 oxides and chlorides, and moreparticularly, inorganic oxides and chlorides of Group 13 and 14 atoms.In other embodiments, support materials may include silica, alumina,silica-alumina, magnesium chloride, graphite, and mixtures thereof. Inyet other embodiments, support materials may include magnesia, titania,zirconia, montmorillonite (as disclosed in EP 0511665B1, for example),phyllosilicate, and the like. Also, combinations of these supportmaterials may be used, such as, for example, silica-chromium,silica-alumina, silica-titania, and the like. Additional supportmaterials may include those porous acrylic polymers described in EP0767184 B1.

In some embodiments, the support materials comprise silica, particularlyamorphous silica, and most particularly high surface area amorphoussilica. Such support materials are commercially available from a numberof sources. Such sources include the Davison Chemical Division of W.R.Grace and Company which markets silica support materials under the tradenames of Davison 952 or Davison 955, or Crosfield Limited which marketssilica support materials under the trade name of Crosfield ES70. In someembodiments, the silica may be in the form of spherical particles, whichmay be obtained by a spray-drying process.

The silica supports may have a wide range of pore sizes and surfaceareas. In some embodiments, the support may have a pore volume of about0.5 to about 6.0 cm³/g and a surface area of about 200 to about 600m²/g. In other embodiments, the support may have a pore volume of about1.1 to about 1.8 cm³/g and a surface area of about 245 to about 375m²/g. In some other embodiments, the support may have a pore volume ofabout 2.4 to about 3.7 cm³/g and a surface area of about 410 to about620 m²/g. In yet other embodiments, the support may have a pore volumeof about 0.9 to about 1.4 cm³/g and a surface area of about 390 to about590 m²/g.

The supports may be contacted with the catalytic moiety in any of theways known to one of ordinary skill in the art. The deposition of acatalytic moiety onto the support surface is usually carried out betweena support in a solid phase and the catalytic moieties in a liquid phase.The support and catalysts are contacted for a time sufficient to supportthe catalytic moieties onto the particulate support. The supportedcatalyst is then washed and dried, producing a solid particulateheterogeneous catalyst.

Following catalyst manufacture, heterogeneous catalysts are typicallystored until needed. To maintain flowability of catalysts used in someembodiments disclosed herein, the catalyst may be stored in aconditioned storage space, for example. Applicants have advantageouslyfound that storing the heterogeneous catalyst in a conditioned storagespace where the temperature is regulated may improve flowability of thecatalyst. The storage space should be maintained at a temperature belowthe critical flow temperature of the catalyst, and may be maintained ata temperature ranging from 1-25° C., from 5-21° C., or from 10-20° C.,for example. The storage space may be conditioned or cooled by any meansknown to one of skill in the art. The catalyst may be stored in aconditioned storage space until needed, at which point the catalyst maybe loaded into the catalyst feed system.

In some embodiments, the catalysts may not be stored, and may bedirectly transported from a catalyst preparation vessel to a catalystfeed vessel.

Applicants have advantageously found that maintaining the temperature ofthe catalyst feed vessel below the critical flow temperature of acatalyst may improve the flowability of the catalyst through thecatalyst feed system. For example, a catalyst, either stored ortransported, may be loaded into a catalyst feed vessel and maintained ata temperature below the critical flow temperature of the catalyst. Invarious embodiments, the catalyst feed vessel may be maintained at atemperature of 29° C. or less, 28° C. or less, 27° C. or less, 26° C. orless, 25° C. or less, 20° C. or less, or 15° C. or less

Applicants have also found that regulating the temperature of thecatalyst feed system, or portions thereof, below a critical flowtemperature of a catalyst, may improve the catalyst flowability anddecrease plugging and other issues related to flowability. For example,portions of the catalyst feed system that may be maintained below acritical flow temperature of a catalyst may include feed valves, piping,tubing, and other catalyst feed system components that may otherwiseattain a temperature above a critical flow temperature of a catalyst,inclusive of all catalyst feed system components between the catalystfeed vessel and the polymerization reactor. In various embodiments ofthis disclosure, the catalyst feed system, or selected portions thereof,may be maintained at a temperature of 29° C. or less, 28° C. or less,27° C. or less, 26° C. or less, 25° C. or less, 20° C. or less, or 15°C. or less.

In some embodiments, such as where only the catalyst feed vessel and/orselect portions of the catalyst feed system are maintained at atemperature below a critical flow temperature of a catalyst, thetemperature set point may be selected so as to account for heat gain viathose portions that are not maintained at a temperature below a criticalflow temperature of a catalyst. For example, where only the catalystfeed vessel is maintained at a decreased temperature, the temperatureset point may be selected such that the catalyst, during transport fromthe catalyst feed vessel to the reactor, may remain below the criticalflow temperature of the catalyst.

Embodiments of the catalyst feed systems of this disclosure may includemajor components such as shown in FIG. 1, including: a catalyst feedvessel 5, which includes at least a catalyst hold tank 10 and mayinclude a catalyst feeder 20; a catalyst supply point 15; a catalystfeeder drive 30; and a heat exchange system 38. The heat exchange system38 may include one or more of tubes, coils, sheets, jacketing, andinsulation. The tubes, coils, or sheets may have a cross-section of anyshape, for example, circular, rectangular, trapezoid, or oval. Anyconventional catalyst feed system may be improved as shown in thepresent disclosure.

The catalyst supply point 15 is connected to the catalyst feed vessel 5and serves to supply the catalyst feed system with catalyst. Thecatalyst feed vessel 5 includes at least a catalyst feeder 20. In someembodiments, a catalyst hold tank 10 is operatively connected to thecatalyst feeder 20, and may deliver catalyst to the catalyst feeder 20.The catalyst feeder 20 is, in turn, connected to the catalyst feederdrive 30, and serves to aliquot a measure of catalyst into the catalystfeeder drive 30. The catalyst feeder drive 30 is fluidly connected tothe polymerization reactor (not shown) and serves to dispense catalystintermittently into the polymerization reactor. Various control valves(not shown) may also serve to maintain low level continuous flow of thecatalyst to the reactor. For example, where the catalyst feed vessel 5includes a catalyst hold tank 10, a feed control valve may be used toeffect the transfer of catalyst from the catalyst hold tank 10 to thecatalyst feeder 20. Another feed control valve may be used to effect thetransfer of catalyst from the catalyst feeder 20 to the catalyst feeddrive 30.

The catalyst feed systems also includes a cooling system for temperatureregulation of the catalyst feed vessels, including the catalyst feedvessel 5. The cooling system may include a heat exchange system 38and/or 43, which may be wrapped around the catalyst feed vessel 5,(i.e., vessel tracing), for example. Where the catalyst feed vessel 5includes a catalyst hold tank 10, either the catalyst hold tank 10 orthe catalyst feeder 20 may be traced by the heat exchange system.Alternatively, both the catalyst hold tank 10 and the catalyst feeder 20may be traced by the heat exchange system 38 and/or 43. The heatexchange systems 38 and 43 serve to cool and maintain the temperature ofthe catalyst feed system below a critical flow temperature bycirculating cooling medium to remove heat from the catalyst feed vessel5 via conduction.

As illustrated, the vessel tracing is not included on the removableportion between catalyst hold tank 10 and catalyst feeder 20. Thistracing may be excluded for reasons such as ease of maintenance andvessel cleaning, for example. In other embodiments, this portion may betraced, insulated, or jacketed so as to decrease heat gain experiencedby the catalyst during transport from catalyst hold tank 10 to catalystfeeder 20.

The cooling system disclosed herein may also include cooling conduits35, 40, and 45, and optionally a chiller 25. The cooling system may beclosed loop or single pass. A closed loop system may provide economicand environmental advantages, as it allows for the recycle and reuse ofthe cooling medium.

The chiller 25 may be any of those known in the art. In some embodimentsof the present disclosure, the chiller system 25 may be a vent recoverychiller, a vortex cooler, or alternatively, a stand alone chiller. Thesedifferent types of chiller systems may be chosen for a particularembodiment based on the availability of cooling medium, the heat load ofthe particular catalyst feed system, or due to cost considerations.

The chiller 25 provides cooling medium to cool the catalyst feed vesselsof the present disclosure. The chiller 25 is connected to the catalystfeeder 20 by cooling conduit 35. The cooling medium is cooled by thechiller 25 and is then pumped from the chiller 25 through the coolingconduit 35. The cooling conduit 35 may be made of any material suitablefor transporting the cooling medium without heat gain before the contactwith the catalyst feeder 20. The cooling conduit 35 may be made ofmaterials commonly used in flow lines, such as copper or stainlesssteel, and may be insulated to prevent ambient heat gain from thesurroundings. The cooling conduit 35 may alternatively be made of aninsulating material such as PVC or some other polymeric material.

The cooling conduit 35 supplies cooling medium to heat exchange systems38 and 43, which serve to cool the catalyst feed vessels (catalyst feedvessel 10 and catalyst feeder 20) by indirect heat exchange. The coolingmedium, as illustrated, is routed through the cooling conduit 35 to thebottom of the catalyst feeder 20. In other embodiments, the tracing maybe top down.

The cooling medium is then routed through heat exchange systems 38, 43,which may wrap around the catalyst feed vessels. In some embodiments,the heat exchange systems 38, 43 may each be a single continuous coil.In other embodiments, the heat exchange systems 38, 43 may includemultiple coils fed from conduits 35, 40, respectively, the coilswrapping around the catalyst feed vessels. The catalyst feed vessels andthe heat exchange systems 38, 43 should be made of material whichencourages heat transfer. In some embodiments, the catalyst feed vesselsmay be made of steel, stainless steel or other metal alloys that allowfor efficient heat transfer. In some embodiments, the heat exchangesystems 38, 43 are made of steel or stainless steel, and in otherembodiments, the heat exchange systems 38, 43 are made of copper.Material selection may also be made based upon the corrosivity of thecatalyst and/or cooling medium.

In some embodiments, the heat exchange systems 38, 43 may have adiameter of ⅜ inch. In other embodiments, the heat exchange systems 38,43 may have a diameter of ¼ inch, ½ inch, or any other commerciallyavailable size of pipe. Those of skill in the art would appreciate thatthe heat exchange systems 38, 43 may have any diameter, but shouldensure that the resulting pressure drop is acceptable.

The heat exchange systems 38, 43 may be wrapped around the catalyst feedvessels 10, 20 in any manner which allows sufficient heat transfer fromthe catalyst feed vessels to the heat exchange systems 38, 43. In someembodiments, the heat exchange systems 38, 43 may be wrapped around thecatalyst feed vessels in a corkscrew configuration, as shown. In otherembodiments, the heat exchange systems 38, 43 may run vertically up anddown the length of the catalyst feeder 20, such as in U-shapedconfigurations around the exterior walls of the catalyst feeder. Thoseof ordinary skill in the art will appreciate that the exactconfiguration of the heat exchange systems is not essential, and anyconfiguration known to achieve the desired heat transfer may be used inembodiments of this disclosure.

As the cooling medium travels through the heat exchange systems 38, 43around the catalyst feed vessels 10, 20, the cooling medium may gainheat by conduction, radiation, or convection from the catalyst feedvessels and the surroundings. In some embodiments, heat transfer cementmay be applied to the heat exchange systems and the catalyst feedvessels 10, 20 to adequately distribute the cooling effect. Any heattransfer cement known in the art may be used, such as, for example,THERMON T-85, available from Thermon Manufacturing Co.

The heat gain by the cooling medium is accompanied by a concomitant heatloss from the catalyst feeder 20. The catalyst feeder 20 and the heatexchange systems 38 may be insulated to prevent unwanted heat gain fromthe atmosphere or from nearby equipment. Insulation of the catalyst feedvessels and cooling coils ensures that the majority of the heat gain bythe cooling medium originates from the catalyst feed system, therebyensuring efficiency of the cooling system. The catalyst feed vesselsshould be able to withstand the lower temperatures and any moisturegenerated by the cooling system. Additionally, any paint or coatingsused in or on the catalyst feed vessels should be able to withstandthese low temperatures and condensation in order to prevent corrosion.

Various vents and drain valves may be provided for safety, maintenanceand operation of the cooling system. For example, cooling conduit 45 maybe connected to breakout fittings and to a vent valve 50 to theatmosphere. Other valves, such as 41, 55, and others, may also be used.

In embodiments where a closed loop cooling system is used, the coolingmedium then travels back to the chiller 25 via conduit 53. In someembodiments, where the chiller 25 is a vent recovery system, the coolingmedium in conduit 45 may be routed to a vent recovery systemglycol/water tank. In other embodiments, where chiller 25 is astand-alone chiller, the cooling medium in conduit 45 may be routed tothe stand-alone chiller. In yet other embodiments where chiller 25 is avortex cooler, cooling medium in conduit 45 may be routed to the vortexcooler. Additional conduits may be provided to route cooling medium usedto cool other various catalyst feed system components into conduit 53,which forms the inlet stream for the chiller 25. The cooling medium maythen be cooled by the chiller system, and re-circulated through thecooling system as needed. Temperature probes (not shown) may beinstalled on the forward conduit 35 and return cooling conduit 45 at thepoints where the conduit enters and leaves the catalyst feed vessel.This allows the monitoring of the temperature of the cooling system toensure that the heat is being removed from the catalyst feed system. Inother embodiments, where a single pass cooling system is used, thecooling medium may be transported via conduit 45 to a disposal vessel.

In some embodiments, only the catalyst feeder 20 is cooled. In theseembodiments, the cooling conduit 40 may then be connected to the chiller25, closing the cooling loop. Alternatively, where a single pass chilleris used, the cooling conduit 40 may be connected to a vessel fordisposal of the spent cooling medium. Those of ordinary skill willappreciate the variety of configurations of the individual components ofthe catalyst feed systems which can be employed in the practice of thepresent invention.

Other embodiments of the improved catalyst feed system of thisdisclosure have major components, such as shown in FIG. 2, including: acatalyst feed vessel 10 and catalyst feed lines 80.

FIG. 2 shows catalyst feed line 80 from the catalyst feed vessel 20 tothe polymerization reactor 90. The catalyst feed lines may be made ofany material known to one of skill in the art. For example, the catalystfeed lines may be made of stainless steel or copper tubing. The catalystfeed vessel 20 may be of the types disclosed in FIG. 1 and describedabove.

In conventional polymerization systems, the catalyst feeder may belocated some distance away from the polymerization reactor due to safetyconsiderations, plant design, or retrofitting. In such cases, thecatalyst may have to travel tens or hundreds of feet to arrive at thepolymerization reactor. During the journey from the catalyst feed vesselto the polymerization reactor, the catalyst may be exposed to heatsources and may undergo undesirable heat gain. This heat gain may be anycombination of ambient heat gain from the air surrounding the feed line,radiant heat gain from nearby machinery such as pumps, heat from thepolymerization reactor 90, heat gain due to friction within the catalystfeed line 80, and so on.

The catalyst feed line 80 may be cooled to prevent the catalystundergoing undesirable heat gain. The cooling of the catalyst feed lines80 may be achieved by any of the means known to one of ordinary skill inthe art. For example, the lines may be insulated, or encased withcooling sleeves, or traced with heat exchange systems. Cooling mediumsuch as air, water, glycol/water mixtures and the like may be circulatedthrough these cooling sleeves or heat exchange systems. As the catalystpasses through the catalyst feed line, any heat gain may be dissipatedvia the cooling medium, and thus preventing undue heat gain by thecatalyst while in transit from the catalyst feed system to thepolymerization reactor. Insulating the catalyst feed line also preventsundue heat gain from the surroundings by providing a non-conductivebarrier layer between the catalyst and the heat sources. In embodimentswhere the catalyst feed system is cooled, the cooled catalyst may bemaintained at a temperature below the critical flow temperature of thecatalyst until delivered to the polymerization reactor 90.

In some embodiments of the present disclosure, the catalyst feed systemsdisclosed herein may be installed as a retrofit to a current plantinfrastructure. In other embodiments, cooling systems disclosed hereinmay be hard built into the catalyst feed system of a new reactor. Insuch a case, jacketed vessels and piping may be used in lieu of tracing.

The cooling medium circulated through the heat exchange system should beable to absorb and transport heat from the catalyst feed system. Coolingmedium useful in embodiments of this disclosure may be any of thoseknown in the art such as, for example, water, glycol, a water/glycolmixture, air, other gases, liquid gases inclusive of liquid nitrogen andliquid carbon dioxide, liquid alkanes, any refrigerants, or a mixturethereof Where air is the preferred cooling medium, a vortex cooler maybe used to cool and direct the compressed air. In a vortex cooler,compressed air is separated into hot and cold streams. The cold streamcan be directed into the heat exchange systems to cool the catalystfeeder and catalyst feed vessel. However, vortex coolers are lessefficient than chiller systems, are a source of noise pollution, use alot of air, and air tends to have poor heat transfer. Nonetheless,vortex coolers are useful for inexpensive spot cooling in situationswhere compressed air is available.

In some embodiments of the present disclosure, where the cooling mediumis a liquid, chiller useful in embodiments disclosed herein may be astand-alone chiller used to cool and direct the cooling medium. Thechiller may be single pass or closed circuit. The stand-alone chillershould be able to withstand harsh outdoor conditions. In someembodiments, the chiller is located above the catalyst feeder level. Inthese embodiments, the chilled vessels will be at a high elevation andthe chilled tubing will require an anti-siphon system. In anotherembodiment, the chiller may be located on the same level as the catalystfeed vessel.

For an exemplary heat load of 252 Kcal/hr for the catalyst feed system(calculated under conditions of 40° C. peak summer temperature, 20 mphwind speed, 2 inch thick insulation on the catalyst feed vessels, and adesired 20° C. catalyst temperature) the smallest stand-alone chillerpackage available in the U.S. might be large for the heat load. Becausethe cooling load is low, the stand-alone chiller compressor may startand stop an unacceptable number of times. The insulation thickness maybe adjusted to ensure an adequate heat load for the stand-alone chiller.Alternatively, a single pass chiller where the cooling medium is drainedand not returned to the stand-alone chiller may be used.

Water is an inexpensive and widely available cooling medium and issuitable for use with a stand-alone chiller. The water may be distilledto remove minerals which may cause scaling in the heat exchange systems,or may be used without distillation. In some embodiments, water may bemixed with a chemical additive to improve flow properties or heattransfer properties. For example, water may be mixed with a glycol suchas ethylene glycol. Ethylene glycol is widely used as automotiveantifreeze and has a low freezing point. Mixtures of water and ethyleneglycol therefore have a lower freezing point than water alone. Thefreezing point depends on the percentage of ethylene glycol in themixture and may range from −1.1° C. at 5% ethylene glycol to −33° C. at50% ethylene glycol. The chemical additive may be any of those known inthe art to provide a superior cooling medium when mixed with water.

In other embodiments, cooling medium may be supplied from an existingvent recovery system, or an existing cooling system. In embodimentswhere a cooling medium from an existing system is used, a line may beinstalled from the existing system to the catalyst feed system. Ifsufficient head pressure is not available from the existing system todrive the cooling medium flow, a booster pump may be installed toprovide the necessary pressure.

A booster pump may also be installed at the catalyst feed level toensure adequate flow. The booster pump may be any of those known in theart. For example an air operated metal diaphragm pump such as a Wildenmodel PRO-FLO P-200, 1″ ADVANCED™ metal Pump with WIL-FLEX diaphragmsinstalled at the catalyst feed levels to ensure adequate flow. The airsupply to the booster pump may also be adjusted by the use of a needleor globe check valve to control the flow of pump discharge or coolingmedium. A check valve may also be installed on the pump discharge toprevent backflow.

The conduits and connections among the various elements of the catalystfeed system are common and well known to those skilled in the art. Thediameter of the conduits may range anywhere from 12.7 mm (0.5 inch) andabove. Preferably the conduits and connections have smooth,corrosion-resistant inner walls which will withstand a harsh chemicalenvironment. In some embodiments, the conduits and connections are madeof stainless steel tubing. The diameter of the catalyst supply valveopenings will depend upon the diameter of the feed conduit, fill chamberof the catalyst feeder, and delivery conduit. In some embodiments, thefeed conduit and delivery conduit will have a diameter ranging betweenabout 63 mm (2.5 inch) to 25.4 mm (1.0 inch), more preferably betweenabout 63 mm (2.5 inch) to 12.7 mm (0.5 inch). The control valves may betypical pneumatically or electrically actuated valves known to those ofordinary skill in the art. Their number and placement within the systemis not critical to the practice of the present invention. Those ofordinary skill will appreciate the wide variety of control arrangementswhich can be employed in the practice of the present invention.

The catalyst feed system may be cooled prior to the addition ofcatalyst. In some embodiments, the catalyst feed system may be cooledfor one day, two days, three days, four days, or more, prior to additionof catalyst to the catalyst feed system, inclusive of the catalyst feedvessels. The catalyst feed system may be continually cooled by thecooling system.

Once the catalyst feed system has been adequately cooled, the catalystmay be loaded, thus negating the need for an extensive cooling periodand possible exposure of the catalyst to temperatures in excess of thecritical flow temperature. The catalyst, for example, may be removedfrom the conditioned storage space or from the catalystpreparation/storage vessel, and loaded into the pre-cooled catalyst feedvessels.

Referring again to FIG. 1, in a class of embodiments of the presentdisclosure, operation of the catalyst feed system is generally astepwise process. The catalyst is first loaded into the catalyst feedvessel 10 via the catalyst supply point 15. The catalyst supply point 15is connected to the catalyst feed vessel 10 and serves to introducecatalyst into the catalyst feed vessel 10. The loading of theheterogeneous catalyst into the catalyst loading point 15 is usuallyperformed under a dry and inert atmosphere to prevent any poisoning ofcatalyst by moisture present as humidity in the air, or by oxygen foroxygen sensitive catalysts. The catalyst flows from the catalyst supplypoint 15 into the cooled catalyst feed vessel 10.

The temperature of the catalyst feed vessel 10 is maintained below 29°C. In some embodiments, the catalyst feed system is maintained at atemperature lower than 25° C., lower than 20° C., lower than 15° C.,lower than 10° C.

The chambers of the catalyst feed vessel 10 and catalyst feeder 20 maybe configured in any way best suited to withstand the particularpressures used. Likewise, the gas used may be any gas; however, an inertgas such as nitrogen is preferred. Those of ordinary skill willappreciate that the exact configuration of the catalyst feed system isnot essential; however, certain elements are of particular importance asdescribed above.

Any ambient heat absorbed by the catalyst during loading or any heat offriction generated by loading can dissipate into the walls of thecatalyst feed vessel where it may be removed by the continually flowingcooling medium. The removal of heat by the cooling medium allows thecatalyst to be kept at or close to its conditioning temperature. This isadvantageous where the catalyst is known to possess good flowability atits conditioning temperature. Because any heat gain is allowed todissipate to and is removed by the cooling medium, the temperature ofthe catalyst may be maintained at a sufficiently low value to preventany agglomerization of particles which may lead to clogging of feedlines and conduits. As such, the catalyst, on leaving the catalyst feedvessel 10, should possess good flowability.

The catalyst supply valve between the catalyst feed vessel 10 and thecatalyst feeder 20 is opened and the pressure in the catalyst feedvessel 10 is used to promote transfer of a quantity of catalyst from thecatalyst feed vessel 10, through the feed conduit and the catalystsupply valve into the cooled fill chamber of the catalyst feeder 20. Inthe embodiment illustrated by FIG. 1, the amount of catalyst to bedelivered to the reactor is determined by the volume of the fill chamberof the catalyst feeder 20. A metering device or the like mayalternatively be used to deliver a measured quantity of catalyst fromthe catalyst feed vessel 10 to the fill chamber of the catalyst feeder20.

The catalyst supply valve between the catalyst feed vessel 10 and thecatalyst feeder 20 is then closed and the feed control valve between thecatalyst feeder 20 and the catalyst feed drive 30 is opened therebyallowing the catalyst portion within the fill chamber of the catalystfeeder 20 to flow to the reactor through feed drive 30. Because any heatgain is allowed to dissipate to and is removed by the cooling mediumfrom the catalyst feed system, the temperature of the catalyst may bemaintained below the critical flow temperature of the catalyst toprevent any agglomerization of particles in the catalyst feeder 20.Agglomerization of particles may lead to clumping of the catalyst whichin turn may lead to clogging of feed lines and conduits. Because thecatalyst is continually cooled, the catalyst should possess goodflowability on leaving the catalyst feeder 20. Once the catalyst portionhas been aliquoted to the catalyst feed line, the feed control valve isclosed. The entire sequence is then repeated as necessary.

Catalyst feed systems described herein may be used for feeding catalystin any polymerization system. Particularly, catalyst feed systemsdescribed herein may be used to maintain the catalyst within at least aportion of a catalyst feed system below a critical flow temperature ofthe catalyst. Such catalyst feed systems may be used with anyheterogeneous catalysts or catalyst systems suitable for use in suchcatalyst feed systems.

For a typical commercial reactor, the heat load may be calculated basedon specific site conditions. Factors to consider when calculating theheat load include solar heat flux under peak summer conditions,convective heat gain at wind velocities at the elevated structures ofthe polymerization system, radiant heat gain from the rector wall, andconduction through insulation. As such, the heat load of each siteshould be calculated to ensure adequate cooling of the catalyst feedsystem or portions thereof.

The cooling of the catalyst during the catalyst feed process has beenobserved to increase flowability. Without desiring to be bound to anysingle theory, it is believed that heterogeneous catalysts which maybecome tacky or sticky at elevated temperatures demonstrate enhancedflowability when used in catalyst feed systems as described herein.

Static generation may also an area of concern for gas phasepolymerization reactions. It is known that high levels of static aredeleterious to continuous operation. Static can be generated by avariety of means, including conveying of dry catalyst through thecatalyst feed system. It is believed that increased static adhesion mayoccur in various catalyst systems at elevated temperatures. Staticadhesion of catalyst particles to the various parts of the catalyst feedsystem or to other catalyst particles may prevent accurate delivery ofspecific catalyst amounts to the polymerization reactor. Withoutdesiring to being bound to any single theory, it is believed that theuse of catalyst feed systems as described herein may additionally reducestatic, leading to improved flowability.

EXAMPLES

It is to be understood that while the invention has been described inconjunction with the specific embodiments thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention. Other aspects, advantages and modifications will be apparentto those skilled in the art to which the invention pertains.

Therefore, the following examples are put forth so as to provide thoseskilled in the art with a complete disclosure and description of how tomake and use the compounds of the invention, and are not intended tolimit the scope of that which the inventors regard as their invention.

Example 1

A metallocene catalyst, XCAT™ HP-100 Metallocene Catalyst, was suppliedcommercially by Univation Technologies, LLC, Houston, Tex. This catalystsystem could benefit from improved flowability under certain operatingconditions, for example, when used in tropical climates. The catalystcylinders were stored in a refrigerated container at 15° C. A catalystfeed system of the present disclosure was installed so as to maintainthe catalyst feed vessel at a temperature below 27° C.

A thin aluminum shroud was installed around the catalyst feed vessel.Compressed air at a pressure of 7 barg was used as a heat exchangemedium and was routed from an existing network to the vicinity of thecatalyst feed vessel. The air supply was split into three feed lines andeach was connected to an Exair CABINET COOLER™ 4840. The cold airexhaust from each Exair CABINET COOLER™ was routed with plastic hosingto exhaust into the annulus space between the catalyst feed vessel andthe aluminum shroud. The three cold air feed lines were approximately120° apart around the circumference of the catalyst feed vessel. At thetop of the catalyst feed vessel, the chilled air was allowed to exit theannulus space.

The vortex coolers were operated with full air supply and an airtemperature approximately 15° C. colder than the supply air temperaturewas achieved. Measured surface temperatures of the catalyst feed vesselranged between 19 and 23.5° C. during the polymerization run.

No plugging of the catalyst injection tubes or the pick-up block wasobserved during the entire run. This was in marked contrast to priorruns without use of a cooling system.

Example 2

A metallocene catalyst, XCAT™ EZ-100 Metallocene Catalyst, was suppliedcommercially by Univation Technologies, LLC. This catalyst system couldbenefit from improved flowability under certain operating conditions,for example, when used in tropical climates.

The catalyst cylinders were stored in a refrigerated container at 10° C.A catalyst feed system of the present disclosure was installed so as tomaintain the catalyst feed vessel and the catalyst feeder reservoir at atemperature below 27° C.

A chilled glycol/water flow from an existing vent recovery system wasused to provide the cooling medium. A 1″ line was installed from theglycol/water line of the existing vent recovery system up to thecatalyst feed level. A Wilden model PRO-FLO P-200 ADVANCED™ Metal Pumpwas outfitted with WIL-FLEX™ diaphragms and installed at the catalystfeed level to ensure adequate flow. The pump discharge of cooling mediumwas routed to the base of the catalyst feeder. The cooling medium flowwas split into three flow lines and routed with heat exchange systemsmade of copper tracing the catalyst feeder. At the top of the catalystfeeder the three lines were joined back together and a vent valve to theatmosphere added to vent liquid filling the line.

The line from the catalyst feeder was then split into three flow linesand routed with heat exchange systems made of copper from the base ofthe catalyst feed vessel up and around the catalyst feed vessel. At thetop of the catalyst feed vessel the three lines were joined backtogether and a vent valve to the atmosphere added to vent while liquidfilling the line.

From the top of the catalyst feed vessel, the return line was routedback to the vent recovery system glycol/water tank. The 1″ line, thecatalyst feed vessel, and the catalyst feeder were all insulated.

The temperature of the glycol/water at the bottom of the catalyst feederwas cold enough to form ice. The temperature of the return line from thecatalyst feed vessel varied from −5 to −15° C. during the polymerizationrun.

No plugging of the catalyst injection tubes or the pick-up block wasobserved during the entire run. This was in contrast to prior runswithout use of the cooling system.

Advantageously, embodiments disclosed herein may provide for improvedcatalyst flow from a catalyst feed vessel to a polymerization reactor.The improvements in catalyst flow may prevent or decrease the occurrenceof plugging, inconsistent flow, and other issues related to poorcatalyst flowability. By maintaining the catalyst feed vessel and/orcatalyst feed lines below a critical flow temperature of the catalyst,polymerization operations may be improved, resulting in improvedproductivity and decreased reactor down time, among other benefits.

Further, the catalyst system flow through embodiments of the catalystfeed systems disclosed herein may be monitored by instruments whichmeasure the pressure differential across a catalyst pick-up block.Catalyst system flow through some catalyst feed systems of the presentdisclosure, where the catalyst feed systems are maintained at atemperature less than the critical flow temperature, may advantageouslydemonstrate a pressure differential greater than that measured forcatalyst system flow through catalyst feed systems not maintained at atemperature less than the critical flow temperature. This greaterpressure differential may be indicative of an improved flowability ofcatalyst systems through catalyst feed systems maintained at atemperature less than the critical flow temperature. Even further,catalyst system flow through embodiments disclosed herein, where thecatalyst feed systems are maintained at a temperature less than thecritical flow temperature, may demonstrate long-term, predictable,greater pressure differential when compared with that measured forlong-term catalyst flow through catalyst feed systems not maintained ata temperature less than the critical flow temperature. Accordingly,embodiments disclosed herein may provide for enhanced continuity ofoperations.

The phrases, unless otherwise specified, “consists essentially of” and“consisting essentially of” do not exclude the presence of other steps,elements, or materials, whether or not, specifically mentioned in thisspecification, as along as such steps, elements, or materials, do notaffect the basic and novel characteristics of the invention,additionally, they do not exclude impurities and variances normallyassociated with the elements and materials used.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, within a range includes everypoint or individual value between its end points even though notexplicitly recited. Thus, every point or individual value may serve asits own lower or upper limit combined with any other point or individualvalue or any other lower or upper limit, to recite a range notexplicitly recited.

All priority documents are herein fully incorporated by reference forall jurisdictions in which such incorporation is permitted and to theextent such disclosure is consistent with the description of the presentinvention. Further, all documents and references cited herein, includingtesting procedures, publications, patents, journal articles, etc. areherein fully incorporated by reference for all jurisdictions in whichsuch incorporation is permitted and to the extent such disclosure isconsistent with the description of the present invention.

While the invention has been described with respect to a number ofembodiments and examples, those skilled in the art, having benefit ofthis disclosure, will appreciate that other embodiments can be devisedwhich do not depart from the scope and spirit of the invention asdisclosed herein.

What is claimed is:
 1. A catalyst feed system for the polymerization ofolefins comprising: a catalyst feed vessel; and a heat exchange systemfor maintaining a temperature of a catalyst system within the catalystfeed vessel, wherein the catalyst feed vessel is jacketed, the heatexchange system comprising fluid connections for supplying a coolingmedium to the vessel jacket and wherein the cooling medium is at leastone of air, liquid nitrogen, liquid carbon dioxide, glycol, water,liquid alkanes, refrigerants and a mixture thereof.
 2. The catalyst feedsystem of claim 1, wherein the heat exchange system traces the catalystfeed vessel.
 3. The catalyst feed system of claim 1, further comprisinga chiller for maintaining a temperature of a cooling medium supplied tothe heat exchange system.
 4. The catalyst feed system of claim 1,further comprising a heat exchange system for maintaining a temperatureof catalyst within a catalyst feed line fluidly connecting the catalystfeed vessel and a polymerization reactor.
 5. The catalyst feed system ofclaim 1, further comprising insulation over at least a portion of thecatalyst feed vessel and heat exchange system.
 6. The catalyst feedsystem of claim 1, further comprising at least one instrument formonitoring flowability.
 7. The catalyst feed system of claim 1, whereinthe heat exchange system maintains the temperature of the catalyst feedsystem at a temperature of 27° C. or less.